The invention relates to a combined quenching and scrubbing system for the cooling and cleaning of crude gases from an entrained flow gasification plant, in which fuel dusts are reacted with oxygen and moderators such as steam or carbon dioxide at temperatures between 1200-1900° C. and pressures up to 10 MPa to give a crude gas rich in CO and H2.
Fuel dusts are understood to mean finely ground coals of different carbonization level, dusts formed from biomasses, products of thermal pre-treatment, such as cokes, torrefaction products and fractions having high calorific values from communal and commercial residual and waste materials. The fuel dusts can be supplied to the gasification as a gas/solid or liquid/solid suspension. The gasification reactors can be provided with a cooling screen or with a refractory lining, as shown by the patent documents DE 4446803 and EP 0677567. In various systems introduced in industry, crude gas and the molten slag can be discharged separately or together from the reaction space of the gasification apparatus, as described, for example, in DE 19718131.
Entrained flow gasification, because of the fuel particles ground to a dust and short reaction times in the gasification space, causes an elevated dust content in the crude gas. Depending on the reactivity of the fuel, this entrained dust consists of soot, unconverted fuel particles and fine particles of slag and ash. The size varies between coarse particles having diameters greater than 0.5 mm and fine particles having a diameter down to 0.1 μm. The separability of the particles from the crude gas depends on this diameter, but also on the composition thereof. In principle, a distinction can be made between soot and ash or slag particles, soot particles generally being smaller and more difficult to separate from the crude gas. Slag particles have a higher density and hence better separability but, in contrast, have a higher hardness and hence erosive action. This leads to increased wear in the separators and crude gas-conducting lines, and can cause safety-relevant leaks and lifetime restrictions. For the removal of the dusts resulting from the fuels, various scrubbing systems are being used.
The prior art to date is described in patent document DE 102005041930 and in “Die Veredlung von Kohle” [The Addition of Value to Coal], DGMK, Hamburg, December 2008, Schingnitz, chapter on “GSP-Verfahren” [GSP Processes]. According to this, the crude gasification gas leaves the gasification space together with the slag formed from the fuel ash at temperatures of 1200-1900° C. and is cooled in a downstream quench space by injection of excess water and freed of the slag and, to a small extent, of entrained dust, it being possible for the quench space to be configured as a cavity quencher or provided with a crude gas-conducting central tube. A cavity quench system is disclosed, for example, in DE 102007042543, in which the crude gas that leaves the gasification space is sprayed with water and drawn off in the lower section beneath a roof construction.
DE 102006031816 exhibits a clear quench space entirely without internals, with injection of quenching water at one or more levels in such an amount that the crude gas is cooled and saturated with steam, and the excess quenching water is drawn off in the lower section alone or together with deposited slag. Variants with a central tube are disclosed by the patents DE 19952754, in which the central tube takes the form of a Venturi tube, DD 145860, in which the crude gas at the end of the central tube is subjected to additional scrubbing in the form of an airlift pump, and DD 265051, where elements for distribution of the crude gas flowing out at the end of the central tube are supposed to ensure uniform flow outward. CN 101003754 B describes an immersed quenching apparatus with a central tube, in which the hot crude gas from the gasification reactor is conducted together with the likewise hot slag downward into a water bath and flows upward as a gas/water suspension within the annular gap of the guide tube, which takes the form of a double tube. The gas/water separation takes place at the upper end of the guide tube. The gas/water suspension which flows upward in the annular gap is said to protect the inner central tube from overheating.
The solution according to patent document DE 102007042543 has the disadvantage that the cavity, as a result of pipelines of relatively high diameter for the removal of crude gas and the roof construction, offers deposition surfaces for entrained slags and dusts, which, as experience has shown, leads to blockages. DE 102006031816 requires homogeneous flow of the hot crude gas out of the gasification space, because there could otherwise be the risk of thermal overloading of the pressure-bearing vessel walls. The arrangement of a Venturi tube according to DE 19952754 can lead to unwanted variations in pressure in the gasification space, and these can barely be compensated for by means of control technology because of their short duration of action. Internals in the quench space and scrub space, as in the patents DD 265051 and DD 224045, can lead, as a result of the puzzolanic properties particularly of the fine dust components in the case of particular coal and ash types, to accumulating deposits having the strength of cement, which likewise lead to blockages and to an increase in pressure drop. This risk likewise exists in the solution according to CN 101003754 B. Should the gap between the inner and outer tubes of the central tube become blocked, the hot crude gas will flow downward in the uncooled inner tube, which can lead to the thermal destruction thereof and additionally endangers the pressure casing of the quench space as a result of overheating.